Aberrant glycosylation accompanies some of the other mutations commonly observed in carcinomas. It has been estimated that about 80% of all carcinomas express the truncated glycans, the Tn Antigen and the sialylated form, Sialyl Tn (STn). With few exceptions, Tn and STn are not expressed in normal, healthy tissues. Furthermore, the non-human immunogenic sialic acid, N-glycolylneuraminic acid (Neu5Gc), seems to be differentially expressed on carcinomas such as breast cancer in the form of Neu5Gc-STn (GcSTn).
Multiple aberrant glycosylation forms have been described in human cancers, identifying specific glycans as a class of cell surface molecules suitable for specific tumor targeting (Cheever, M. A. et al., Clin Cancer Res. 2009 Sep. 1; 15(17):5323-37). For example, various human cancer types (such as bladder, breast, cervical, colon, lung, and ovarian cancer among others) show high expression of STn antigen, which is rare in normal human tissues (Karlen, P. et al., Gastroenterology. 1998 December; 115(6):1395-404; Ohno, S. et al, Anticancer Res. 2006 November-December; 26(6A):4047-53). In addition, the presence of STn on tumor-associated mucins relates to cancer with poor prognosis and is therewith considered an attractive epitope for cancer detection and targeted therapy (Cao, Y. et al., Virchows Arch. 1997 September; 431(3):159-66; Julien, S. et al., Br J Cancer. 2009 Jun. 2; 100(11):1746-54; Itzkowitz, S. H. et al., Cancer. 1990 Nov. 1; 66(9):1960-6; Motoo, Y. et al., Oncology. 1991; 48(4):321-6; Kobayashi, H. et al., J Clin Oncol. 1992 January; 10(1):95-101). Tn and STn formation is associated with somatic mutations in the gene Cosmc that encodes a molecular chaperon required for the formation of the activate T-synthase (Ju, T. et al., Nature. 2005 Oct. 27; 437(7063):1252; Ju, T. et al., Cancer Res. 2008 Mar. 15; 68(6):1636-46). It can also result from increased expression of the sialyl transferase, ST6GalNAc-I (Ikehara, Y. et al., Glycobiology. 1999 November; 9(11):1213-24; Brockhausen, I. et al., Biol Chem. 2001 February; 382(2):219-32). De-novo expression of STn can modulate carcinoma cells, change the malignant phenotype, and lead to more aggressive cell behaviors (Pinho, S. et al., Cancer Lett. 2007 May 8; 249(2):157-70). Although STn is highly expressed in malignant tissues, low levels are also found on healthy human cells (Jass, J. R. et al., J Pathol. 1995 June; 176(2):143-9; Kirkeby, S. et al., Arch Oral Biol. 2010 November; 55(11):830-41). STn alone has attracted attention as a target for cancer detection and therapy (Cheever, M. A. et al., Clin Cancer Res. 2009 Sep. 1; 15(17):5323-37). STn is also present in mucins associated with cancer stem cells (Engelmann et al., Cancer research, 2008, 68, 2419-2426) and STn is implicated in immune suppression (Carrascal, M. A., et al., Molecular Oncology. 2014. 8(3): 753-65).
In addition to the presence of STn, other glycosylation changes have been described in cancer. One of them involves Neu5Gc. N-acetylneuraminic acid (Neu5Ac) and Neu5Gc are the two major sialic acids on mammalian cell surfaces. Neu5Ac and Neu5Gc differ only in that Neu5Gc comprises an additional oxygen atom associated with chemical group attached to carbon 5. Due to the loss of a functional gene, humans can only synthesize sialic acid in the form of Neu5Ac, but not Neu5Gc. However Neu5Gc can be metabolically incorporated into humans from animal-derived dietary sources such as red meats (Tangvoranuntakul, P. et al., Proc Natl Acad Sci USA. 2003 Oct. 14; 100(21):12045-50; Nguyen, D. H. et al., J Immunol. 2005 Jul. 1; 175(1):228-36; U.S. Pat. No. 7,682,794, U.S. Pat. No. 8,084,219, US2012/0142903, WO2010030666 and WO2010030666). Neu5Gc is significantly abundant among human tumors (Higashi, H. et al., Cancer Res. 1985 August; 45(8):3796-802; Miyoshi I. et al., Mol Immunol. 1986. 23: 631-638; Hirabayashi, Y. et al., Jpn J Cancer Res. 1987. 78: 614-620; Kawachi. S, et al., Int Arch Allergy Appl Immunol. 1988. 85: 381-383; Devine, P. L. et al., Cancer Res. 1991. 51: 5826-5836; Malykh, Y. N. et al, Biochimie. 2001. 83: 623-634 and Inoue, S. et al., 2010. Glycobiology. 20(6): 752-762) and remarkably low in normal human tissues, which had been overlooked for several decades (Diaz, S. L. et al., PLoS One. 2009. 4: e4241; Tangvoranuntakul, P. et al., Proc Natl Acad Sci USA. 2003. 100: 12045-12050; Varki, A. et al., Glycoconj J. 2009. 26: 231-245). The increased metabolic accumulation of diet-derived Neu5Gc in cancer tissue compared to healthy human tissues is likely explained by at least three factors: rapid growth with underproduction of competing endogenous Neu5Ac, enhanced macropinocytosis induced by growth factors (Dharmawardhane, S. et al., Mol Biol Cell. 2000 October; 11(10):3341-52; Simonsen, A. et al., Curr Opin Cell Biol. 2001 August; 13(4):485-92; Johannes, L. et al., Traffic. 2002 July; 3(7):443-51; Amyere, M. et al., Int J Med Microbiol. 2002 February; 291(6-7):487-94), and the upregulation of gene expression of the lysosomal sialic acid transporter gene sialin by hypoxia (Yin, J. et al., Cancer Res. 2006 Mar. 15; 66(6):2937-45). In addition, all humans tested to date comprise a polyclonal antibody reservoir against non-human Neu5Gc, which makes it the first example of a xeno-autoantigen (Padler-Karavani, V. et al., Glycobiology. 2008 October; 18(10):818-30; Varki, N. M. et al., Annu Rev Pathol. 2011; 6:365-93). The accumulation of dietary Neu5Gc in malignant tumors in the face of an anti-Neu5Gc response was shown to facilitate tumor progression by inducing a low-grade chronic inflammation (Hedlund, M. et al., Proc Natl Acad Sci USA. 2008 Dec. 2; 105(48):18936-41). Thus, Neu5Gc containing glycan epitopes on human tumors represent a valuable possibility for drug targeting. A recent study suggests the existence of antibodies against Neu5Gc-containing STn (GcSTn), but not Neu5Ac-STn (AcSTn), in cancer patients and explores their potential as a specific biomarker for cancer detection (Padler-Karavani, V. et al., Cancer Res. 2011 May 1; 71(9):3352-63).
There remains a need in the art for antibodies capable of binding glycans, including glycans associated with disease and diseased cells and tissues. Such antibodies could be used to target tumor cells and cancerous tissues and to treats subjects suffering from cancer. Further, there remains a need for better methods to develop such antibodies as well as methods for specific characterization of epitopes bound by glycan-interacting antibodies. The present invention meets this need by providing antibodies that target glycans, by providing methods of developing anti-glycan antibodies, and by providing methods of using anti-glycan antibodies to identify and target cancerous cells and tissues in the diagnosis and treatment of disease.